Madagascar ragwort - the end of extensive pastoral farming
Senecio madagascariensis, known as Madagascar ragwort, and fireweed in Australia, is an invasive yellow flowering daisy. The plant has multiple germinations throughout the year and seeds spread rapidly— locally mainly via wind and regionally as a contaminant or ‘hitchhiker’.
It takes only six weeks to set seed from germination and one mature plant will produce more than 10,000 seeds. It readily invades pastures longer than 42-day round lengths due to the aggressive seeding and is capable of germinating all year round following any warm rain event.
It is highly toxic to cattle and horses, causing irreversible liver damage. Sheep and goats are more tolerant of the toxins and are known to graze the plant.
There is no simple single approach that effectively controls all life stages – a combination of attention to detail (i.e. pulling juvenile plants), pasture improvement, pasture management and repeated intensive herbicide controls are usually required to bring well-established infestations under control.
The weed is widespread north of Kerikeri. If the spread continues around the North Island at the rates we’ve seen in the Far North, New Zealand could see a huge loss in production for farming businesses.
Invasive spread of Madagascar ragwort on Rangiputa Farm
Colin Rakena, Rangiputa Farm Manager, says that while Madagascar ragwort has been a persistent issue, infestations have recently accelerated exponentially.
A combination of climatic factors, a critical mass of the plant in the region, and the farm transitioning to efficient bull systems have seen the weed become a significant challenge on the Far North farm.
It is now present on between 1,200 and 1,400 hectares of the farm's 3,300 hectares. Most of the infestation is in cattle-only pastures, some cells covered by as much as 50%. This has contributed to a dramatic 35% drop in productivity for the farm over the past six years.
“It is spreading into areas with sheep now and even they can’t control it. Within the past three years, the problem has grown six-fold.”
Control attempts
Efforts to control the spread on Rangiputa have involved a combination of manual pulling, herbicide spraying, and mixed grazing.
The farm has trialled multiple herbicide combinations, such as Kamba (dicamba), Sprinter/Amine (MPCA), and Bonza (uptake oil), but these methods have only yielded limited short term success.
Herbicide treatments have proven to be prohibitively expensive, costing between $150 and $900 per hectare annually. Spraying was found to also kill beneficial pasture species like clovers and makes regrowth more palatable to livestock, resulting in high toxicity levels among cattle and stock deaths.
While sheep have been reintroduced in hopes of reducing the weed's spread, they have not been successful in curbing Madagascar ragwort.
Colin Rakena, the farm manager, believes that a comprehensive spraying programme across the entire affected area may be necessary to control the weed, but acknowledges the logistical challenges and high costs involved.
Broader implications for New Zealand farming
Madagascar ragwort is not just a local issue for Rangiputa Farm but is spreading across much of the Northland region, including farms and lifestyle blocks.
As climate change impacts regions around the country, those facing hot, dry summers are at particular risk of the plant spreading and taking hold.
Pāmu Chief Operating Officer Will Burrett says:
“There is a real need there to fund an effort to investigate a longer-term solution in biological controls. It poses a very real risk to the future of pastoral farming, not only in Northland, but well beyond here.”
Future action needed
The experience at Rangiputa Farm underscores the urgent need for a coordinated, multi-agency response to consider biological controls to effectively manage and control Madagascar ragwort before it further impacts New Zealand's agricultural productivity.
